Japanese patent document JP-A-2003-123514 discloses a headlamp device for a vehicle comprising a headlamp having a swivel mechanism for swinging the lighting fixture unit from side to side and a drive controlling unit for driving and controlling the swivel mechanism of the lighting fixture unit.
The headlamp device for the vehicle disclosed in the foregoing patent is arranged to cause the drive controlling unit to drive the swivel mechanism according to the velocity of the vehicle and the steering angle so that the lighting fixture unit swings in the turning direction of the vehicle.
When such a swivel control is performed, the light beam can be emitted along the road ahead of the vehicle in the forward direction even while turning, making it possible to enhance the front viewability during turning.
It is desirable for the light beam to be emitted toward the driver viewing point (i.e., the point at which the driver is looking during operation) on the road ahead of the vehicle in the forward direction. However, the driver viewing point may vary with the curve turning radius (i.e., the radius of the running curve around which the vehicle is turning) or the velocity of the vehicle.
Accordingly, the vehicle velocity and the steering angle are used as parameters to calculate the curve turning radius, which is then used with the vehicle velocity to calculate the angle of the direction of the driver viewing point relative to the forward direction of the vehicle (hereinafter referred to as “driver viewing point angle”). The driver viewing point angle is then used to determine the corresponding target swivel angle over which the lighting fixture unit is swung.
Problems may arise because operation of the drive controlling unit becomes difficult. It is also disadvantageous because a vehicle velocity sensor and a steering angle sensor are needed to perform such drive control.